I assume that what you really want, is a new data table, where each row represents the mean of 3 minute intervals from the original data table.
I would do it this way.
Create a new column in the original data table. Set the formula for the new column to
if(row()==1, start = :time);
floor((:time - start) / in minutes(3));
This will create a new column where the values are in 3 minute bins.
Now all you need to do, is to use the Summary Platform
Tables=>Summary
to create the new data table. Just specify your new bin column as the Group column and the means for the measurement columns.
Jim